Download 2.3 - 2.5 - Chemistry

mass p ≈ mass n ≈ 1840 x mass e1
Atomic number, Mass number and Isotopes
Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Isotopes are atoms of the same element (X) with different
numbers of neutrons in their nuclei
Mass Number
A
ZX
Atomic Number
1
1H
235
92
2
1H
U
Element Symbol
(D)
238
92
3
1H
U
(T)
2
The Isotopes of Hydrogen
3
How many protons, neutrons, and electrons are in
14 C
?
6
6 protons, 8 (14 - 6) neutrons, 6 electrons
How many protons, neutrons, and electrons are in
11 C
?
6
6 protons, 5 (11 - 6) neutrons, 6 electrons
4
The Modern Periodic Table
Noble Gas
Halogen
Group
Alkali Metal
Alkali Earth Metal
Period
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Chemistry In Action
Natural abundance of elements in Earth’s crust
Natural abundance of elements in human body
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A molecule is an aggregate of two or more atoms in a definite arrangement held
together by chemical forces
H2
H2O
NH3
CH4
A diatomic molecule contains only two atoms
H2, N2, O2, Br2, HCl, CO
diatomic elements
A polyatomic molecule contains more than two atoms
O3, H2O, NH3, CH4
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An ion is an atom, or group of atoms, that has a net positive or negative charge.
cation – ion with a positive charge
If a neutral atom loses one or more electrons
it becomes a cation.
Na
11 protons
11 electrons
Na+
11 protons
10 electrons
Cl-
17 protons
18 electrons
anion – ion with a negative charge
If a neutral atom gains one or more electrons
it becomes an anion.
Cl
17 protons
17 electrons
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A monatomic ion contains only one atom
Na+, Cl-, Ca2+, O2-, Al3+, N3-
A polyatomic ion contains more than one atom
OH-, CN-, NH4+, NO3-
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Common Ions Shown on the Periodic Table
10
How many protons and electrons are in
?
27Al 3+
13
13 protons, 10 (13 – 3) electrons
How many protons and electrons are in
?
78 Se 234
34 protons, 36 (34 + 2) electrons
11